Synthetic filament having antistatic properties

ABSTRACT

Novel synthetic filament having antistatic properties comprising a continuous nonconducting sheath of synthetic polymer surrounding a conductive polymeric core containing carbon black.

United States Patent 1 1 p 11 1 3,803,453

Hull Apr. 9, 1974 SYNTHETIC FILAMENT HAVING ANTISTATIC PROPERTIES [56] References Cited [75] Inventor: I Donald Robert Hull, Wilmington, UNITED STATES PATENTS I 3,678,675 7/1972 Klein 317/2 C 7 Assigneez E L du p m d Nemours and 3,639,807 2/1972 McCune 1. 317/2 C 3,582,445 6/1971 Okuhashi.... 57/157 AS Company wllmmgton 3,551,279 12/1970 Ando et al. 161/175 [22] Filed: June 19, 1973 [2]] App]. No.: 371,507 Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, .lr. Related U.S. Apphcation Data 63 Continuation-inart of Ser. No. 273,793, Jul 21, 1 1972, abandoned y [57] ABSTRACT Novel synthetic filament having antistatic properties 317/2 57/157 6 comprising a continuous nonconducting sheath of syn- 161/175, 317/2 C, 139/426 R thetic polymer surrounding a conductive polymeric 51] Int. Cl. 05f 3/00 ore containing carbon black, [58] Field of Search I. 317/2 R, 2 C; l6l/l75;

5 /1 7 AS 20 Clalms, 2 Drawmg Flgures 1 SYNTHETIC F ILAMENT HAVING ANTISTATIC PROPERTIES CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 273,793 filed July 21, 1972 now abandoned.

BACKGROUND OF THE INVENTION 3,639,807; such wire in the face yarn tends to lose effectiveness as it bends and becomes pressed down into the carpet.

SUMMARY OF THE INVENTION This invention provides a novel synthetic filament having antistatic properties comprising a continuous nonconductive sheath of a synthetic, thermoplastic, fiber-forming polymer surrounding an electrically conductive core comprised of electrically conductive carbon black dispersed in a thermoplastic, synthetic polymer, said sheath comprising at least 50 percent of the filament cross-sectional area (i.e., at least 50 percentby volume) and said filament core having an electrical resistance of less than ohms per inch at a direct current potential of 2 kilovolts. For use'at low concentrations in admixture with other filaments, the filaments of the invention preferably have a core resistance of less than 10 ohms/inch at a direct current potential of 2 kilovolts. Preferably, said filaments have a molecularly oriented sheath as the result of attenuation during spinning and/or drawing in the course of their preparation.

Highly conductive core compositions, i.e., those containing more than percent by weight of said carbon black are preferably employed in filaments having a sheath content of at least 80 percent.

The present invention permits antistatic filaments which may be used in light-colored textile goods. For such end-uses the sheath comprises at least 90 percent of the filament and the sheath is delustered to partially conceal the black core such that the filament has a light reflectance value as described herein of greater than 20 percent. A preferred delustered filament contains 2 to 7 percent by weight of titanium dioxide pigment in the sheath.

By appropriate selection of the sheath polymer, antistatic fibers of this invention may be dyed as desired, cobulked under a variety of conditions and employed in end uses where sheath toughness comes into play. The fibers of this invention avoid the dangers of too high electrical conductivity. They also possess a high level of crush-resistance as compared with for antistatic purposes.

Surprisingly, in spite of the fact that a major portion of the filament consists of the nonconducting sheath whichacts as electrical insulation, the filaments of this invention can be effectively employed for antistatic protection independent of relative humidity as a very minor component of a fabric, yarn or other textile material comprised predominantly of other synthetic fibers or filaments needing antistatic protection. Accordingly, the invention also comprehends antistatic yarn and staple fibers comprised of a mixture of nonconducting synthetic filaments and less than 20 percent by weight of the mixture of filaments of the invention described heretofore. Concentrations of filaments of the invention in such mixtures can provide excellent antistatic performance even when present at concentrations of less than 2 percent, but preferably the mixtures contain at least about 0.05 percent by weight of wire used said filaments. In such mixtures the sheath polymer may be mutually dyeable with the nonconducting filaments; more specifically, it may be of the same polymeric class or genus as the polymer of the nonconducting filaments, e.g., nylon sheath fiber with nylon homofiber.

The invention is also directed to a process for the preparation of cospun antistatic filaments comprising the steps of cospinning in a sheath/core filament configuration an electrically conductive core composition comprised of an electrically conductive carbon black dispersed in a thermoplastic synthetic polymer surrounded by a nonconductive sheath composition of a synthetic, thermoplastic, fiber-forming polymer, said composition being spun in such proportion that said sheath composition comprises at least 50 percent by volume of said filaments.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view of a sheathcore filament of the invention.

FIG. 2 is a schematic cross-sectional view of an antistatic yarn comprised of a mixture of filaments of the type depicted in FIG. 1 and nonconducting, synthetic filaments.

In the filament cross-section 5 depicted in FIG. 1, the core material 1 comprises a conductive composition of carbon black 3 dispersed in a polymer matrix 4 surrounded by a sheath material 2 comprising a nonconducting polymer.

In FIG. 2, filaments of cross-section 5 of the type of FIG. 1 are among the substantially greater number of nonconducting synthetic filaments 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The nonconductive sheath" of the filaments of the invention is comprised of a synthetic, fiber-forming polymer. The filaments have a surface filament resistance that is greater than 10 ohms per inch as measured by contacting the subject filament surfaces at low direct current voltages, e.g., of volts or less. Homofibers of such sheath materials would also have resistances greater than 10 ohms per inch measured accordingly. The term fiber-forming is used in the conventional sense to denote linear, high molecular weight polymers which can be formed into fibers of sufficient strength and toughness to be useful.

Compared to the high resistance, nonconductive sheath, the core of the filaments will have a low resistance and high electrical conductivity once electrical contact therewith is established either by the use of electrodes which penetrate the sheath and directly contact the core or by the use of surface contacting electrodes and the application of a sufficiently high voltage to electrically break down the sheath and thereby establish electrical contact with the core. With regard to the latter, i.e., the use of surface contacting electrodes, as an applied DC voltage is increased to several hundred and particularly several thousand volts, a point will occur at which a noted or sudden increase in current will begin to flow as described in the test procedure herein. Once conductivity has been established in this way, the current usually continues to flow even when the voltage is reduced to a lower level, provided filament contact with the electrodes of the measuring device is not altered.

The low resistance properties exhibited by the core of these filaments is evidence that the core maintains its electrical continuity throughout the length of the filament being measured. Breaks in the core continuity between the measuring electrodes are evidenced by a much higher electrical resistance approaching that of the sheath. Occasional breaks in core continuity are found not to be significantly detrimental to the antistatic performance of the filaments of this invention. Preferably, however, the'core remains continuous throughout the entire length of the fibers and filaments of the invention whether they be staple or continuous filaments. It is essential that the core remain continuous for a sufficiently long length along the filament to establish an effective antistatic network in combination with other such antistatic filaments. Filaments having the specified degree of core conductivity when tested by the methods described herein are found to provide highly effective antistatic protection. The filamentsheath may consist of any extrudable, synthetic, thermoplastic, fiber-forming polymer or copolymer. This includes the polyolefins, such as the polyethylenes and the polypropylenes, polyacrylics, polyamides and polyesters of fiber-forming molecular weight. Particularly suitable sheath polymers are the condensationpolyamides of diamines and dicarboxylic acids and those of amino acids; the condensation polyesters, particularly those of terephthalic or isophthalic acids and lower glycols such as ethylene glycol, tetramethylene glycol and hexahydro-p-xylene' diol; and the poly(acrylonitriles). Such polymers may be modified as to their dye receptivities as is known in the art, e.g., by copolymerization to incorporate basic or acidic dye sites, to facilitate their blending and mutual dyeing with other dyed or dyeable synthetic fibers.

Tensile and other physical properties of the filaments of the invention are primarily dependent on the sheath polymer. For high strength filaments, polymers of higher molecular weight and those permitting higher draw ratios are used in the sheath. While undrawn filaments of the invention may provide adequate strength for some purposes, the drawn filaments are preferred.

The sheath thickness must be sufficient to provide the desired protection to the core, e.g., strength and heat and abrasion resistance as well as to assist in visu ally hiding the core where this is important. In general, a sheath thickness of at least 3 microns is desired, with greater thicknesses being governed by the filament denier or diameter which can be used. Suitable sheath thicknesses for normal textile deniers are in the range of 8 to 22 microns. In some applications, for example where the filaments of the invention are to be subjected to high temperature processing with other filaments such as in hot fluid jet bulking or other texturing operations, it is essential that the sheath have a sufficiently high melting point to avoid undue softening or melting under such conditions. For such applications,a higher melting sheath polymer such as poly(hexamethylene adipamide) is preferred over poly(e -caproamide).

The filament core consists of a conducting carbon black dispersed in a polymeric, thermoplastic matrix material. The core material is selected with primary consideration for conductivity and processability. Carbon black concentrations in the core of 15 to 50 percent may be employed. It is found that 20 to 35 percent provides the preferred level of high conductivity while retaining a reasonable level of processability. The use of known, specially prepared more highly conducting carbon blacks are helpful in minimizing the amount required.

Due to the tendency of high loadings of carbon black to reinforce or stiffen plastic compositions, for preparation purposes the softer, lower melting (also lower second order transition temperature) polymeric core matrix materials are preferred to stiffer higher melting ones. The core polymer is preferably lower melting than the sheath polymer with a lower second order transition temperature than that of the sheath. It is, not essential that the core composition be capable of being spun into filaments by itself and therefore the core polymer need not be fiber-forming. The core polymer should be thermally stable and extrudable under the conditions required for spinning the sheath polymer. Suitable core matrix polymers include those selected from the polyamides, polyesters, polyacrylics, polyethers, polycaprolactone, and polyolefins (e.g., polypropylene, low and high density polyethylenes). The polymers may be blended with other materials such as oils and waxes to facilitate processing. Copolymers may also be employed such as poly(ethylene/vinyl acetate) copolymers.

The carbon black may be dispersed in the core polymer by known mixing techniques. Care must be exercised to avoid overmixing and consequent loss in conductivity while still achieving a sufficiently uniform dispersion of carbon black in the core polymer to permit extrusion and spinning. Carbon black containing compositions useful for forming the core in spinning of the filaments of the invention preferably will have a specific resistance of less than 200 ohm-centimeters, and more preferably less than 50 ohm-centimeters.

For satisfactory spinning it is important to remove volatile material from polymers into which the carbon black has been added, prior to melt spinningyThis may be done during or after compounding the carbon black with the polymeric matrix material. It can be helpful to vacuum dry such polymers for example for 16 hours under slight vacuum at 68C. Standard precautions to prevent oxidative degradation during spinning such as the exclusion of oxygen with inert gas in polymer lines, etc. are employed.

The cross-sectional area (which relates directly to filament volume) of the conductive core in the composite filament need only be sufficient to impart the desired resistance properties thereto and may be as low as 0.5 percent by volume. The lower limit is governed primarily by the capability of manufacturing sheath/core filaments of sufficiently uniform quality while maintaining adequate core continuity at the low core volume levels.

Spinning of the filaments of the invention can be accomplished by conventional two-polymer sheath/core spinning equipment with appropriate considerations for the differing properties of the two components. They are readily prepared by known spinning techniques and with polymers as taught for example in US. Pat. Nos. 2,936,482. 2,989,798 contains additional teaching of such spinning with polyamides.

Conventional drawing processes for the filaments can be used but care should be exercised to avoid sharp corners which would tend to break or damage the core. In general, hot drawing, i.e., where some auxiliary filament heating is employed during drawing, is preferred. This tends to soften the core material further and aid drawing of the filaments. These antistatic filaments may be plied with conventional synthetic, undrawn filaments and codrawn.

The subject filaments are readily prepared having a tenacity of at least 1.5 grams per denier, which is quite adequate when said filaments are blended as a minor component with other filaments. The subject filaments preferably have an elongation-at-break of at least percent and less than 150 percent. The resulting textile properties are dependent primarily upon the properties of the other filaments of the blend.

For general applications the filaments of this invention have a denier per filament( dpf) of less than 50 and preferably less than 25 dpf.

The filaments may be of round or non-round, eccentric or concentric sheath/core configurations and combinations thereof. The concentric configuration provides maximum protection and hiding of the core. The fineness of the core greatly aids in its concealment, and the filaments with fine cores can be employed in dyed or patterned textile goods with no other concealing factor. Further concealment where needed is realized by the presence of an opacifier such as voids or a white, solid, particulate delusterant such as titanium dioxide pigment in the sheath. Non-round filament configurations, e.g., multilobal, tend to further conceal the core.

Among variables which affect concealment of the core are sheath thickness and dyeability, sheath/core ratio,'concentration of delustrant such as titanium dioxide in the sheath, and also voids formed by separation of the sheath and core which is found in oriented filament having dissimilar sheath and core polymers, such as a polyamide sheath anda polyethylene core.

Without a concealing sheath to hide the blackness, carbon black filled fibers generally have a light reflectance of less than 5 percent. Reflectance levels above about 20 percent, which can be achieved with this invention, provide a very significant improvement in avoiding coloration problems from the subject filaments in lightly dyed goods.

The filamentsof this invention are capable of providing excellent antistatic protection in all types of textile end uses including knitted, tufted, woven and nonwoven textiles. They may contain conventional additives and stabilizers such as dyes and antioxidants. They may be subjected to all types of textile processing including DESCRIPTION OF THE TEST PROCEDURES Filament Core Resistance Filament core resistance is determined from current flow measured at 2 kilovolts on a 2-inch sample length. Suitable apparatus is a 15 KV Biddle Dielectric Tester (James G. Biddle Company, Plymouth Meeting, Pennsylvania). A three filament bundle is clamped straight between pairs of electrodes 2 inches apart and a sufficiently high voltage is applied to achieve current flow (e.g., 1-4 KV). When current flows, the voltage is adjusted to 2 KV and the yarn resistance is calculated from the current flow according to Ohms Law where R E/l. For example, if at 2 KV the current flow is 10 microamps for the 2-inch sample, the resistance for the three filaments is 10 ohm/inch. Resistance per filament is then'3 X 10 ohms/in. To achieve current flow as above, the voltage should be increased gradually to avoid a sudden current surge which may burn out the filaments. Burn-out is readily detected visually by broken or fused or charred filaments) and such samples should be disregarded. The resistance of filaments of lengths less than 2 inches can be measured by appropriately adjusting the distance between the electrodes.

Reflectance Light reflectance, the lightness or whiteness of the specimen as compared to a magnesium oxide standard, is measured using a pnotoelectric reflection meter. A suitable apparatus is the Photoelectric Reflection Meter Model 610 with a green tristimulus filter Catalog No. 6130), Search Unit Model 610-Y and a white enamel working standard calibrated having a -75 percent reflectance (Catalog No. 6162), obtainable from the Photovolt Corp., Madison Avenue, New York, New York 10016. The conductive filament sample to be measured is wound on 2-inch by 3-inch black mirror cards (approximately six layers of filaments) and the reflectance is measured from the cards (average of 10 measurements).

Percent Core in the Filament Percent core by volume is most conveniently determined by comparing the cross-sectional area of the black core to the total filament by measuring under a microscope. This is conveniently done at a magnification of about 400x. For round filaments this can readily be calculated from the ratio of the square of the core diameter to the square of the total filament diameter. The average of 10 determinations is used to compensate for irregularities. For nonround cross-sections, measurements taken on photographs of filament crosssections at a known magnification permit ready calculation.

Where the sheath polymer is sufficiently different in solution properties from the core that it can be removed by differential solvent action, the percent core material can be determined gravimetrically by dissolving the sheath and comparing the weight of the insoluble core to the weight of the original sample. For example, formic acid can be used to dissolve a 66-nylon sheath from a polyethylene core.

Specific Resistivity Test of Core Material The specific resistance of the core material containing carbon black is determined by measuring the DC. resistance across a two-inch length of a film strip of the sample 1 inch wide, and having a thickness of about 0.01 inch. Such films are conveniently prepared by pressing a powder or pelletized sample of the core material between two sheets of aluminum foil in a press, heated above the melting point under a pressure of 20,000 psig. for 1 to 2 minutes. After cooling, the foil is siripp'eariam the saniiilfilm' and 1-inch wide strips about 2.5-3 inches long are cut from the sample. The

. thickness of the film is measured with a micrometer. A

strip is clamped between two copper electrodes spaced two inches apart and the DC. resistance measured with an ohmmeter. Specific resistance of the film in ohmcm. is calculated from the instrument reading in ohms as the product of the measured resistance times the width times the thickness all divided by the sample length, all in centimeter units.

Percent Carbon Black in Core Standard analytical methods can be employed for determining the concentration of carbon black in the filament or core material. A method suitable for use on ethylene plastics containing carbon black is described in or can be derived from the ASTM Method D1603-68. This is a thermogravimetric method suitable for use in the absence of any nonvolatile pigments or filler materials other than carbon black.

EXAMPLE 1 Concentric sheath/core filaments are prepared having a sheath of 45 RV 66-nylon and a polyethylene core containing 20 percent extra-conductive furnace black. The carbon black is an oil furnace black, extraconductive Vulcan XC-72, (Fixed Carbon 98 percent, Volatiles 2 percent, Particle Size 30 millimicrons, Electrical Resistivity lowest) available from the Cabot Corp., 125 High St.,' Boston, Mass. 02110. This black is described in their Technical Bulletins S-8 and 1518/173. The carbon black dispersion is prepared by mixing the carbon black at about 120C. with a low density (0.9T6) poly ethylene resinfrnel t index 23; (Alat hon 2821 by Du Pont), by milling in a dough mixer. The black is added slowly and the mixture cast 10 minutes after completion of addition. This polyethylene resin is selected for its softness. (Other useful resin compositions are a low density (0.919) polyethylene, melt index 1.9 [Alathon 20 by Du Pont] alone and blended 'with to 40 percent of an oil or wax). The molten carbon black mixture is filtered through a 100 X 100 mesh screen and extruded. Pressed films show excellent dispersion and conductivity with a specific resistance of 12.7 ohm-cm. Using this as the core, sheath/core continuous filaments, (three 65 denier monofilaments), are spun at 425 ypm wherein the total I denier is held constant and the core volume decreased by changing pump speeds to produce the items of Table l. The core volume is established from the pumping rate and confirmed by cross-section analysis of the fila ments at 200 X magnification. A 3-hole stainless steel spinneret is used wherein the sheath and core polymers are fed concentrically and individually until emerging at the face of the spinneret. An insert capillary is used to carry the core polymer composition to the spinneret face where it exits surrounded by the sheath polymer The filaments are spun at about 65 'dpf. They are then drawn 3.06X at about 200 ypm ona curved heated plate maintained at 150C. Yarn physical and electrical properties are shown in Table 1.

TABLE 1 Item 1 2 3 4 5 Core Volume 50 40 25 18 12 Yarn (Filament) Denier 21.4 20.6 21.4 21.2 19,9 Tenacity, gpd 1.5 1.9 2.4 2.8 3.4 Elongation, 26.2 36.4 30.3 54.7 57.4 lnitial Modulus, gpd 15.3 17.9 25.1 20.3 25.2 Core Resistance X 10, ohms/inch/ filament 2.5 6.7 4.0 13.3 Breakdown Voltage, KV 1.6 3.4 3.4 4.6 Carpet Static Propensity, KV (as in Ex-' ample 11 2.0 3.0 2.8 3.0 2.6

*As calculated from microamperes measured at 2 kilovolts The test'ca'rpets of Table l are made of a commercial 3700 denier/204 filament 66-ny1on bulked, trilobal, continuous filament carpet yarn in a -inch pile height. One yarn end of the conductive fiber (about 0.56 percent by weight) is plied upon coning with the carpet yarn, and tufted. The visibility of the conductive fila-.

ments decreases noticeably in the carpet with the reduction in core volume.

EXAMPLE 11 Preparation of Sheath Polymer A 317.5 kilogram aqueous solution containing 50 percent by weight of hexamethylene diammonium adipate (66-nylon salt) is charged into a stainless steel vessel to which is added 721 grams of a solution containing 10 percent by weight manganous hypophosphite [Mn( H PO in water; 70 grams of a solution containing 25 percent by weight acetic acid, and 100 m1. of a silicone antifoam 11.2 percent concentration. The charge is concentrated by evaporation to about percent solids by weight and transferred to a stainless steel autoclave equipped with an agitator. The autoclave is purged of air with inert gas and is heated to about 200C. to a pressure of 17 atmospheres. A 14.83 kilogram titanium dioxide (Ti-pure Rutile, Titanium Dioxide R-960, E. I. du Pont' de Nemours & Co., Wilmington, Delaware) slurry prepared as 49 percent by weight in water is charged with agitation into the pressurized autoclave. The heating is continued until the temperature reaches 273C. and the pressure is gradually re- I duced to the atmospheric pressure. The polymerization cycle is continued as in Example I of US. Pat. No. 2,163,636. Upon completion of the polymerization reaction, the molten polymer is extruded in the form of about A inch strands. After quenching with water they are cut into A X 3/ 16 inch chips suitable for remelting in a spinning assembly. The flake has these properties:

Relative viscosity 43.5 (NH 46.0 eq./l0 g.

TiO 5.04%

Mn(H PO 0.048%

Core Polymer Composition (by weight) Polyethylene: 70%

Conductive Carbon of Example I: 30%

Polyethylene. Alathon PE-4318 Low density polyethylene (density 0.916, Melt lndex 23 ASTM-D- 1238) manufactured by E. l. du Pont de Nemours.& Co., for injection molding. It contains 50 ppm antioxidant to improve thermal and aging stability.

Preparation In a 1 gallon capacity double arm dough mixer are charged 1905 grams of polyethylene and 816.5 grams of the carbon black. The composition is mixed for 30 minutes at 140C., extruded, filtered through a 100 X 100 mesh screen and pelletized.

The product shows the following properties:

Specific Resistance: (of a film cast at about 180C.)

2.9 to 4.2 ohm-cm.

% Carbon Black Analysis: 30.2%

% Moisture: 0.04%

If the moisture content is greater than 0.1 percent the pellets should be dried at 70C. and under vacuum for 24 hours before spinning.

Spinning The sheath and core polymers are cospun on a screw melter spinning machine using a spinneret assembly to spin concentric sheath/core filaments bythe technique shown in US Pat. No. 2,936,482.

The sheath polymer is-fed at 19.8 gm./min. (as calculated from pump capacity and speed) and core polymer at 0.7 gm./min. (as calculated from pump capacity and speed) throughputs to provide a concentric sheath- /core composition of 96 percent sheath and 4 percent core by volume. During spinning the sheath and core polymer temperatures in the screw melter are set at:

Sheath Polymer Core Polymer The spinning block temperature is 293C. Both sheath and core polymer supply hoppers are purged with inert gas.

The relative viscosity of sheath polymer as coming from the spinneret (free fall) is about 56, the increased RV resulting from further polymerization of dried 66- nylon in the screw melter. The spinning speed is approximately 890 ypm. The collected spun yarn is gray in color and has these properties:

Finish on yarn: 1.0%

Percent Core, by Volume: 4%

Percent Sheath, by Volume: 96%

Bundle Spun Denier: 60

No. of Filaments/Bundle: 3

Reflectance: 37-40% Drawing The'conductive 60-3 denier spun yarn is drawn on a draw-twisting machine at 2.7X draw ratio, 400 ypm winding speed, and 180C. shoe temperature.

The drawn yarn properties are:

No. of Filaments: 3

Tenacity, gpd: 3.8

Elongation: 35%

Modulus: l3 (gpd at elongation) Core Resistance (Bundle): 4.7 X 10" ohm/inch Reflectance: 34%

Cobulking One end of an approximately 3400 denier, 160 filament nylon 4-void hollow filament yarn of the type shown in Br. Pat. No. 1,292,388 is cobulked with one end of the conductive yarn on one position of the hollow filament spinning machine. The yarns are combined in a hot chest under 10-20 g. tension at the last chest roll wrap before entering the bulking jet. The chest roll is at 195C. and yarn velocity is 1185 ypm. The cobulking is done by passing the yarn through an air jet operated at psig and 240C. as described in Belgium Patent No. 573,230 to produce filaments having random, three-dimensional curvilinear crimp with alternating regions of S and Z filament twist. The yarn is then cooled and passed to windup.

The tensile properties of the cobulked yarn are essentially the same as the unmodified product. Mockdyed level loop carpets k inch pile height, 29.4 ounces/- square yard, 5/32 inch gauge, 7 stiches per inch) made from yarns containing the conductive filaments (test) and from yarns containing no conductive filaments (control) with a commercial nonwoven polypropylene backing (Typar by Du Font) and latexed with a commercial latex give the following static propensities at 20 percent RH and 70F.

Test Control The static test is AATCC Test Method 134-1969 with changes as adopted by the Carpet and Rug lnstitute, September, 1971.

ln greige or mockdyed carpets the 20-3 denier conductive filaments give a very slight blueish cast. Dyed bulked continuous filament carpets containing conductive filaments show no difference in most of the solid color shades and only slight differences in certain solid light colors, e.g., yellow, orange and pink, when compared with the control carpet.

If desired, the filaments of the invention may be used in staple form, e.g., at from 0.5 to 5 percent by weight with nonconductive staple in carpet yarn.

EXAMPLE III This example demonstrates that care must be exercised in drawing filaments of this invention to avoid loss of conductivity.

Filaments are spun of an eccentric sheath/core configuration with a 66-nylon sheath of 44 relative viscosity and containing 0.3 percent TiO and a 6-nylon core (45 relative viscosity 31.8 equiv. NH end groups/ 10 grams) having nominally 20 percent carbon black of the type in Example 1. The filaments are 40 percent core by volume. The 3-filament yarn has a spun denier of about 79. The yarn is cold drawn using a draw-pin. As shown in Table 2, the yarn resistance upon cold drawing is found to increase as a function of the draw ratio. When the yarn is hot drawn without a pin using a curved heated plate at about C., essentially no increase in resistance is encountered. It is speculated that heating of the yarn in a heated draw zone upon drawing permits softening of the core enough to prevent core breakage or disruption of the carbon particle distribution required for conductivity.

TABLE 2 Draw Ratio Core Resistance (ohgns/inch/ '3-filaments 1 (undrawn) 1.5 l 1.5 6.l l0 3.0 5X10 3.0 (hot drawn) 0.7 l0"" *As calculated from the three filaments measured individually.

EXAMPLE IV Sheath Polymer Poly(ethylene terephthalate) flake having a relative viscosity of 23 i 2 measured on 0.8 gm. polymer in ml. of hexafluoroisopropanol at C.

Core Polymer 6-Nylon 22 percent conductive carbon black of Example '1.

Preparation A p're-dispersed slurry of 22.680 kilograms conductive carbon (Cabot XC-72), 86.180 kilograms of cap- I to 7 hours, the pressure is reduced gradually within 1V2 hours from 250 psig to atmospheric pressure (reducing cycle). The polymer is then extruded at 278C. into a continuous ribbon which is quenched with water and cut into Vs inch flake. The flake is washed with water for about 4 hours in a stirred kettle heated at 95C., to

remove monomer. This operation is repeated three times and at the end about 6.3 percent caprolactam is extracted. The polymer is then dried under vacuum (25 inches Hg) until the moisture content is less than 0.3 percent. The flake is remelted, extruded and filtered through a screen filter of increasing mesh (30 to 200) and pelletized, then vacuum dried to less than 0.03 percent moisture content.

The specific resistance of films cast from this polymer varies between 10-60 ohm-cm.

Spinning and Drawing The sheath and core polymers are co-spun and drawn on a coupled spin-draw machine at 1500 ypm windup speed (as calculated from the speed of the windup roll in rpm).

Using a screw melterthe sheath polymer is fed to a spinneret at 29.7 gm./min. (as calculated from denier spun and windup speed) and core polymer at 6.7 gm./min. (as calculated from denier spun and windup speed) throughputs to provide a concentric sheath- /core composition at 81 percentsheath (as calculated from throughputs) and 19 percent core (as. calculated from throughputs) by weight. During spinning the screw melters temperatures are set at:

Sheath Polymer Core Polymer Screw Melter Zone Temperature C. Temperature C. Top 249 206 Middle 281 250 Bottom 289 265 The drawn yarn is black in color and has these properties:

No. of Filaments/Bundle 1 Denier 19.02

Total Finish on Yarn 1.83

Core Resistance 3.3 X 10 ohm/in.

Tenacity, gpd 2.5

Elongation, 39.9 v

Modulus, gpd at 10% Elongation 13.6

EXAMPLE V Sheath Polymer Poly(ethylene terephthalate) flake having an RV of Core Polymer Prepared as in Example II.

Spinning The sheath and core polymers are co-spun as in Example II at 860 ypm. The sheath polymer is fed at 36.3 grams/minute (as calculated from pump speed and capacity) and core polymer 1.38 grams/minute (as calculated from pump speed and capacity). throughputs to provide a concentric sheath/core composition of 96 percent sheath and 4 percent core by volume as determined by measurement of the cross-section under magnification.

During spinning the screw melter temperature for the sheath polymer is set at:

Core Polymer Screw Melter Temperature C.

Zone 1 286 114 (Top) Zone 2 284 184 (Middle) 242 (Bottom) and the spinning block temperature at 292C.

The yarn is spun at 60 denier/ 3 filaments (60-3). Drawing 60-3 Denier sheath/core yarn is drawn at 454 ypm and 3.8X draw ratio and 97C. hot shoe temperature.

The drawn yarn properties are:

Denier 17.2

No. of Filaments 3 Core Resistance, ohm/in./fil. 6.76 X 10 Tenacity, gpd 5.3

Elongation, 21.5

Modulus, M, 43.2 gpd at 10% elongation The sheath/ core test yarn is cotextured with a commercial l50-34-polyester yarn on a Leesoria 570 falsetwist texturing machine. The cotextured yarn (1 end 17.2-3 sheath-core with 1 end -34 polyester) is woven into a Suisse Pique double knit fabric. This fabric is dyedand finished using conventional methods. After 30 washes the fabric is tested on asta tic tester (Presco Scientific Co., electrometer model E525) and compared with the control fabric made from the same polyester yarn alone and processed under identical conditions.

Electrostatic Charge on Fabric (volts) After 0 second After I20 seconds Test Fabric 380 Control Fabric 2750 25 50 Good electrostatic protection for the test item is indicated.

mer as in Example II, and a 6-nylon core polymer con-' taining 28% carbon black prepared as in Example IV. Filaments 96 percent by volume sheath and 4 percent core are drawn 3.0X over a 180C. curved (24 inch) hot plate. The yarn properties are:

Bundle denier 20.2

Tenacity, gpd 3.18

Elongation, 49.1

Modulus, Mi, gpd 24.4

Core Resistance 4.5 X 10 ohm/in.fil.

Reflectance, 32 l Cobulking The conductive yarn is cobulked as in Example II with basic dyeable 1225-68 66-nylon hollow (4 voids) continuous filament carpet yarn (Type 854 Antron II by Du Font) and tufted at A inch pile height, 14 ounces/square yard level loop carpets as outlined in Example II. I

Mockdyed carpet reflectance and static propensity are compared against a control carpet made without conductive yarn.

Carpet Static Carpet Propensity* Reflectance Test 1.5 to 2.4 K Volts 65 Control 8.6 to 9.8 75

* As in Example II Visual rankings of the carpets are in agreement with the measured carpet reflectance.

EXAMPLE VII Filaments (4 ends of 60 spun denier, 3 filaments) having a nylon sheath and a polyethylene core essentially the same as those in Example [I are prepared, for use in staple, having properties as follows:

Finish on Yarn, 0.43

Percent Core, by weight: 3.5%

Percent Sheath, by weight: 96.5%

Percent Carbon in Core: 32.3%

Reflectance: 39%

Bundle (12 fil.) Core Resistance: X ohm/inch The spun yarn is drawn by combining eight ends, on an experimental draw machine at 3.0X draw ratio, 230 ypm. winding speed and 180C. hot shoe temperature.

The drawn yarn properties are:

Bundle denier: 690

No. of Filaments: 96

Tenacity, gpd.: 4.72

Elongation, 18.5

This conductive yarn bundle is cut to approximately 6.5 inch length pieces and blended with commercial Du Pont T-838, 66-nylon carpet staple during carding at 0.6, 2 and 5 percent quantities. The blends are processed under normal staple conditions to make spun yarns of 2.4 cotton count/2 ply, 3.5Z/3.5S twist. The

yarns are heat set in an autoclave and then tufted into 35 oz./square yard, 5/32 inch gauge, A inch pile height saxony style cut pile carpets with a Typar polypropylene backing and latexed with a commercial latex. The carpets are scoured and dyed conventionally with a mixture of 3 commercial yellow, red and blue acid dyes.

The dyed carpets give the following static propensi ties on shuffle test at 20 percent RH and -.70F.

Ratio of Antistat Fiber Carpet Static Propensity,

to Base Fiber Kilovolts 0/100 9.4 0.6/99.4 3.2 2.0/98.0 2.5 5.0/95.0 1.9 as in Example II EXAMPLE VIII having a trilobal cross-section with a modification ratio Items C through I-I have round filament crosssections.

Item C comprises filaments having a 66-nylon sheath containing 5 percent titanium dioxide and a core containing 30 percent carbon black in a polyolefin base comprised of 40 percent polypropylene, 20 percent polyethylene and 10 percent Nordel 1500, a commercial elastomer based on a terpolymer of ethylene, propylene and a non-conjugated diene from E. I. du Pont Nemours and Company.

Item D comprises filaments having a sheath of a commercial polypropylene resin (Shell PWD-15 2) and core composition as in Item A.

Item Eemploys the same sheath as in Item D with a core material consisting of a polycaprolactone commercial resin (Union Carbide PCL-700) containing 30 percent carbon black.

Item F employs a sheath of 66-nylon containing 5 percent titanium dioxide pigment and a core of a commercial polypropylene resin (Hercules 8MSR) containing 25 percent carbon black.

Item G employs a polypropylene sheath as in Item D and a core of a commercial polyethylene ether resin (Du Pont TLF 16815) containing 26 percent carbon black.

Item H is a non-antistatic control item having a nylon sheath as in Item A and the same polyethylene resin core containing no carbon black.

Filament properties for these items are shown in Table 3.

TABLE 3 Percent core (by Yarn Core yarn/ Draw Tenacity, Elong., volume refiec., resist.. Item ratio Denier g./d. percent Mod. mi. X-section) percent ohm/inch/fil.

21.6 2.65 68.4 21.6 10 28.5 3 21.1 3.00 81.8 22.1 35 2.46 110.!) 2.1!] ($2.8 l4.2 3 49 ll 42. 3.6) 120 28.3 7.5 11 ll 104.4 1.72 I50 [4.7 7.4 12.6 0.3 33.3 2.4!! 34.2 17. 7.5 31.3 80 56. 7 3. 2!! lllhl 28. 7 ll 0. 3 19. l 3. 87 34. 5 23. 6 4 10 What is claimed is:

l. A novel synthetic filament having antistatic properties comprising a continuous, nonconductive sheath of a synthetic thermoplastic fiber-forming polymer surrounding an electrically conductive polymeric core comprised of electrically conductive carbon black dispersed in a thermoplastic synthetic polymer, said sheath comprising at least 50 percent of the filament cross-sectional area and said filament core having an electrical resistance of less than 10 ohms per inch at a direct current potential of two kilovolts.

2. The filament of claim 1 wherein the sheath constitutes at least 80 percent of the filament cross-sectional area and the conductive core contains more than percent by weight of carbon black.

3. The filament of claim 1 having a tenacity of at least 1.5 grams per denier.

4. The filament of claim 1 wherein the sheath constitutes at least 90 percent of the filament cross-sectional area.

5. The filament of claim 4 wherein the sheath is at least 3 microns in thickness.

6. The filament of claim 4 wherein the sheath is delustered such that the filament has a light reflectance value of greater than 20 percent.

- 7. The filament of claim 4 wherein the sheath contains from 2 to 7 percent by weight of titanium dioxide as a delusterant.

8. The filament of claim 1 wherein the sheath is 6-6 nylon and the synthetic polymer of the core is 6-nylon.

9. The filament of claim 1 wherein the sheath is a polyamide and the synthetic polymer of the core is polyethylene. v g

10. The filament of claim 1 wherein the sheath is a polyester and the synthetic polymer of the core is polyethylene.

11. The filament of claim 1 wherein the core is lower melting than the sheath.

12. The filament of claim 1 having a denier of less than 50.

13. The filament of claim 1 wherein the filament core has an electrical resistance of less than 10 ohms per inch at a direct current potential of two kilovolts.

14. A continuous filament yarn comprising a mixture of nonconducting synthetic filaments and less than 20 percent by weight of filaments of claim 1.

15. A continuous filament yarn comprising a cobulked mixture of nonconducting synthetic filaments and less than 20 percent by weight of filaments of claim 1.

. 16. A mixture of nonconducting polyamide filaments and less than 20 percent by weight of filaments of claim 1 having a polyamide sheath.

17. A mixture of staple fibers comprising nonconducting synthetic filaments and less than 20 percent by weight of filaments of claim 1. v

18. A carpet wherein the face yarn contains a filament of claim 1.

19. A novel synthetic filament having antistatic properties comprising a continuous nonconductive polyamide sheath surrounding an electrically conductive core electrical resistance of less than 10 ohms/inch at a direct current potential of two kilovolts.

20. A continuous filament yarn comprising a co- I bulked mixture of nonconducting synthetic filaments and less than 20 percent by weight of filaments of claim 

2. The filament of claim 1 wherein the sheath constitutes at least 80 percent of the filament cross-sectional area and the conductive core contains more than 20 percent by weight of carbon black.
 3. The filament of claim 1 having a tenacity of at least 1.5 grams per denier.
 4. The filament of claim 1 wherein the sheath constitutes at least 90 percent of the filament cross-sectional area.
 5. The filament of claim 4 wherein the sheath is at least 3 microns in thickness.
 6. The filament of claim 4 wherein the sheath is delustered such that the filament has a light reflectance value of greater than 20 percent.
 7. The filament of claim 4 wherein the sheath contains from 2 to 7 percent by weight of titanium dioxide as a delusterant.
 8. The filament of claim 1 wherein the sheath is 6-6 nylon and the synthetic polymer of the core is 6-nylon.
 9. The filament of claim 1 wherein the sheath is a polyamide and the synthetic polymer of the core is polyethylene.
 10. The filament of claim 1 wherein the sheath is a polyester and the synthetic polymer of the core is polyethylene.
 11. The filament of claim 1 wherein the core is lower melting than the sheath.
 12. The filament of claim 1 having a denier of less than
 50. 13. The filament of claim 1 wherein the filament core has an electrical resistance of less than 109 ohms per inch at a direct current potential of two kilovolts.
 14. A continuous filament yarn comprising a mixture of nonconducting synthetic filaments and less than 20 percent by weight of filaments of claim
 1. 15. A continuous filament yarn comprising a cobulked mixture of nonconducting synthetic filaments and less than 20 percent by weight of filaments of claim
 1. 16. A mixture of nonconducting polyamide filaments and less than 20 percent by weight of filaments of claim 1 having a polyamide sheath.
 17. A mixture of staple fibers comprising non-conducting synthetic filaments and less than 20 percent by weight of filaments of claim
 1. 18. A carpet wherein the face yarn contains a filament of claim
 19. A novel synthetic filament having antistatic properties comprising a continuous nonconductive polyamide sheath surrounding an electrically conductive core comprised of electrically conductive carbon black dispersed in polyethylene, said sheath comprising at least 90 percent of the filament cross-sectional area and containing from 2 to 7 percent by weight of titanium dioxide as a delusterant and said filament core having an electrical resistance of less than 109 ohms/inch at a direct current potential of two kilovolts.
 20. A continuous filament yarn comprising a cobulked mixture of nonconducting synthetic filaments and less than 20 percent by weight of filaments of claim 19, filaments of said yarn having random, three-dimensional curvilinear crimp with alternating regions of S and Z filament twist. 